Tempreature stabilized chamber utilizing thermoelectric cooling



3, 1964 A. E. ANDERSON ETAL 3,155,157

TEMPERATURE STABILIZED CHAMBER UTILIZING THERMOELECTRIC COOLING FiledAug. 9, 1962 3 Sheets-Sheet 1 INVENTORS Albert E Anderson BY W/l/iam R..Slubsfad Attorneys Nov. 3, 1964 A. E. ANDERSON ETAL TEMPERATURESTABILIZED CHAMBER UTILIZING THERMOELECTRIC COOLING Filed Aug. 9, 1962 v3 Sheets-Sheet 2 L fiH v REFERENCE 0c 'o1TTTQ cT|AMBEQ 58 I I II [5 'l66 l sal THERMOELECTR|C J COOLING DEVICE VOLTAGE AC COMPARATOR 92 9aAMPLIFIER 90 L aa 0c AMPLIFIER ea 00 POWER SUPPLY INVENTORS Albert EAnderson William R. Stubs/ad Af/omeys Nov. 3, 1964 A. E. ANDERSON ETAL3,155,157

TEMPERATURE STABILIZED CHAMBER UTILIZING THERMOELECTRIC QOOLING FiledAug. 9, 1962 3 Sheets-Sheet 5 U Z J D 0 DJ, m ll- J E m m U AMBIENTTEMPERATURE RE 32 333 AT ERATURE z TEMP E AGING AT LOW #52 5518 :00 Q

ELAPSED TIME lNVENTOR-S Albert 5 Anderson William R. .Sfubsfad Afforneys United States Patent Ofitice Faiented Nov. 3, l fid 3 155 157rnrtirnnairnna ens UT;- LEZING 'll-lERMGELEC'li-RR @UQLENKG Albert E.Anderson, Cedar Rapids, and William R.

Stuhstad, lliarion, lows, assignors to Collins Radio Qoinnany, QedarRapids, llowa, a corporation of Iowa Filed Aug. 9, 1962, Ser. No.215,)35 2 ltliaims. (til. led-3%) This invention relates to atemperature stabilized chamber and more particularly to a multichamberdevice that may be accurately maintained at a constant predeterminedtemperature either above or below environmental temperatures. It isoften necessary to provide a chamber that is temperature stablized andthis is particularly true in utiliza tion of some electronic equipments.Such a chamber is often required, for example, to maintain the crystalof a crystal oscillator at constant temperature, since deviation intemperature alfects the output frequency of the oscillator, as is wellknown in the art.

The amount of control needed to maintain operation of an equipmentWithin prescribed limits varies, of course, with the amount ofpermissible error. it relatively wide tolerances are established for acrystal oscillator, for example, little, or possibly no, temperaturecontrol is necessary. However, as the need arises to maintain thefrequency within more stringent limits, temperature must be morecritically controlled.

One of the better expedients for providing temperature control, has beenthrough the use of a stabilizing chamber, or oven. Where the temperatureneed only be controlled within about plus or minus one degreecentrigrade per one hundred degree centigrade temperature change, asingle stage chamber, or oven, can be utilized. However, as thepermissible error limits become more stringent, the need arises forbetter temperature control, which control, it has been found, may beobtained through the use of an additional chamber surrounding the innerchamber.

A multistage chamber, or oven, capable of temperature control withinless than a hundredth of a degree per one hundred degrees change inambient temperatures is shown, for example, in United States PatentNumber 2,973,420.

While ovens have been developed that are capable of maintaining aconstant temperature Within stringent limits, as brought outhereinabove, the constant temperature in such as oven must, however, beat least as high as the highest ambient temperatures expected since theonly control exerted is by heating.

It is therefore an object of this invention to provide a temperaturecompensated chamber capable of maintain ing temperature within thechamber constant which temperature may either be above or below expectedenvironmental temperatures.

More particularly, it is an object of this invention to provide atemperature compensated multichamber device that may be either heated orcooled as required in order to maintain the temperature of the innerchamber within stringent limits.

Still more particularly, it is an object of this invention to provide atemperature compensated multichamber device that utilizes thermoelectriccooling means whereby the temperature within the inner chamber may bemaintained below environmental temperatures, if desired.

By utilizing a thermoelectric cooling device, it has been found that theresulting structure is more compact and reliable than heretofore knownoven devices. it is therefore another object of this invention toprovide a temperature compensated chamber that is highly compact and yetreliable.

It has been found that aging of a crystal also alfects the outputfrequency. It has also been found that if a crystal is maintained atelevated temperatures, aging occurs at a more rapid rate than doescomparable aging where the temperatures are maintained relatively low,hence the provision of means for stabilizing temperature at a relativelylow operational temperature is desirable.

Where temperature must be controlled within very stringent limits, suchas, for example, for a crystal oscillator when used in a frequencystandard to calibrate narow frequency range control communicationssystem, it is not uncommon to require that the output frequency vary nomore than one part in 108 over a considerable period of time. Thus, ifan oven is capable of maintaining the ouput frequency of an oscillatorwithin one part in 10 for 60 days at elevated temperatures, for example,a temperature compensating device capable of maintaining the temperatureat a reduced level (such as 30 centigrade) could greatly lengthen thisperiod of time.

it is therefore another object of this invention to provide atemperature compensated multichamber device capable of maintaining theoutput frequency of a crystal oscillator constant for long periods oftime by decreasing aging of the crystal through maintenance of thecrystal at a relatively low temperature.

With these and other objects in View which will become apparent to oneskilled in the art as the description proceeds, this invention residesin the novel construction, combination and arrangement of partssubstantially as hereinafter described and more particularly defined bythe appended claims, it being understood that such changes in theprecise embodiment of the herein disclosed invention may be included ascome within the scope of the claims.

The accompanying drawings illustrate one complete example of theembodiment of the invention constructed according to the best mode sofar devised for the practical application of the principles thereof, andin which:

FIGURE 1 is a perspective View of the temperature compensating chamberof this invention with portions cut away for illustrative purposes;

FIGURE 2 is an end section view taken through the lines 2-2 of FIGURE 1;

FlGURE 3 shows a typical thermoelectric cooling unit;

FEGURE 4 is a schematic and block diagram illustrating the temperaturecontrol system utilized in the temperature compensated chamber of FIGURE1;

FIGURE 5 is a graph illustrating typically the output requency of acrystal as affected by temperature changes; and

FIGURE 6 is a graph illustrating the effect of crystal aging onfrequency devitations of the oscillator for different operationaltemperatures.

Referring now to the drawings in which like numerals have been used forlike characters throughout, the numeral lll refers generally to thetemperature compensated multichamber device of this invention.

As shown in FIGURES l and 2, a metallic can 14 of copper, for example,has a cylindrical side wall 15, front end wall 16 and rear end wall 17.Walls 1547 define an inner chamber 18 to be maintained at constanttemperature. The component, or element, to be maintained at a constanttemperature is normally placed in the inner chamber 18, and, as shown inFlGURES l and 2, may be a crystal 2%. As is conventional, crystal 2.53may be contained within a glass envelope 21.

As shown best in FIGURE 1, a plurality of coils 24, 25, 26, 2-7 arewound about cylindrical side Wall 15. These coils are connected in theform of a bridge circuit 2-9, as shown in FIGURE 4, for sensingtemperature deviations Within inner chamber 13 and for heating the samewhen necessary, as will be brought out more fully hereinafter.

As shown in FIGURES 1 and 2, can 14 is contained within can 32, whichcan has a cylindrical side wall 33, front end wall 34-, and a rear endwall (not shown). Can 32, like can it, is metallic and is maintainedspaced with respect to can 14, and the area between the cans constitutesan outer chamber 36. As shown by FIG- URES 1 and 2, chamber 36 may becompletely filled by a layer of thermal insulating material 37 (exceptfor the area occupied by coils 24%? around on the outside of side wall15). Insulating layer 37 may be or" conventional material, and may, forexample, be polyurethane foam. As shown in FIGURE 1, side wall 33 alsohas a plurality of coils th, 41, and 43, forming bridge circuit 44 (seeFIGURE 4), wound thereon. Bridge circuit 44 senses deviations intemperature in outer chamber 36, as will be brought out more fullyhereinafter.

Can 32 is covered by an insulating layer 45, which layer may be ofmaterial identical to that of layer 37. A pair of leads 47 and 48 areconnected to crystal 2t through a plug, or conduit which plug extendsthrough front end walls 16 and 24- of inner can 14 and outer can 32,respectively, and the insulating layers. Plug 5i) seals the unit in amanner well known in t. e art.

Coils 2 through 27, forming bridge circuit 29, may be wound on side wall15, as shown in FIGURE 1, with the windings adjacent to one another but,of course, electrically insulated from one another and from side Wall inconventional manner. Windings 25 and 26 are preferably copper, whilewindings 24 and 27 are preferably made of an alloy having temperatureresponsive properties unlike copper. Such an alloy that is usable, forexample, may exhibit an ohmic value change of about 0.6% per degreecentigrade. Bridge circuit 44, consisting of coils ll) through 43, maybe identical to bridge circuit 29, and may have windings 4 1i and 42 ofcopper and windings 4t and 4-3 of alloy.

As shown in FIGURE 1, a lead 54 is connected to one end of windings 24-and 26 of bridge circuit 2? through plug, or conduit 55, while a secondlead 56 is connected to windings 25 and 2] through plug 55. Lead 5d islikewise connected to the free ends of windings 2d and 25 (as indicatedin FIGURE 4) through a long conduit, or plug as, which plug extendsthrough the outer thermal insulation layer 37 to, and through, the backend walls of cans 1d and 32, while lead M is connected to the free endsof windings 26 and 27 through the same plug.

Windings ll through 43 of bridge circuit 44 are connected in a similarmanner. Lead 64 is connected to one end of windings 4t) and 42 throughplug us, while lead us is connected to one end of leads 4-1 and 43through the same plug (which plug, as shown in FIGURE 1, need only passthrough end wall 34 and outer insulation layer 45). Lead 68 is connectedto the free end of windings dil and at (as indicated in FIGURE 4)through long plug or conduit 69, while lead 76 is connected to the freeends of windings 42 and 43 through the same plug (which plug extendsalong the outer insulation layer to the rear wall of can 32 and throughthe same).

It is a feature of this invention that the outer can 32 and hence outerchamber 36 may be cooled as desired. For this purpose, a thermoelectriccooling device 73 is provided. As shown in FIGURES 1, 2 and 3, and as isconventional, thermoelectric cooling device '73 may consist of aplurality of units '74, each of which has a hot junction '75 and a coldjunction 76. These junctions may be aluminum plates and the coldjunction may be formed in such a manner (as shown best in FIGURE 3) soas to snugly receive outer cylinder 33 with the windings 56) throughthereon.

As is conventional, the hot and cold junctions are separated bycylinders 78 alternately of dissimilar metal connected conventionally ina series circuit by copper contacts 79 to provide maximum electricalresistance for the device. The copper contacts may be fastened to thealuminum plates conventionally, such as bonding with cement, forexample, so that the aluminum plates are electrically insulated from thecopper contacts, by thin electrical insulating layer fill. Cylinders '73are preferably made of bismuth telluriae (Bi Te and arranged so that aquantity of heat will be absorbed at the cold junctions and generated atthe hot junctions (Peltier effect) when a DC. voltage is supplied. Adevice exhibiting this effect is shown and described, for example, inUnited States Patent No. 2,984,077.

A blower 81 is provided to circulate air through a heat sink 32, whichheat sink is conti' uous to hot junction 75 of thermoelectric coolingunit, though electrically insulated therefrom by thin electricalinsulating layer 9%.

As shown in FEGURE l, outer thermal insulating coating 4-5 is utilizedto cover the entire unit (with the exception of the blower and itsconduit) including outer can 32 and the thermoelectric units '74.

As shown in FIGURE 4-, the windings of each bridge circuit are connectedto provide automatic temperature compensation. Windings 54 and 56 areconnected to the input side of a conventional AC. amplifier 86, Whilewindings 5% and 61 are connected to the output side of amplifier as. Asis conventional, AC. amplifier 86 may be energized from a DC. powersupply source 88.

Windings 6d and as of bridge circuit are connected to a conventionalvoltage comparator 9d, the output of which is coupled through aconventional DC. amplifier 92 and lead 9 5 to thermoelectric coolingdevice 73. As is conventional, DC. amplifier 92 may be energized fromthe DC. power source The remaining two windings (windings es and 7d ofbridge circuit 44) are connected to a reference voltage and to ground,respectively.

It is tie purpose of the multichamber device of this invention tostabilize and maintain the temperature within the inner chamberconstant, preferably at a low temperature.

As shown by the graph of FIGURE 5, crystal frequency deviates(characteristically in an 8 curve) over a range of temperatures. If thetemperature is maintained at a constant value, however, the crystalfrequency will no longer be subject to variations due to temperaturefluctuations. in addition, and as shown by the graph of FIG- URE 6, andas brought out hereinabove, frequency deviations due to aging of thecrystal are improved considerably by maintaining the crystal at arelatively low temperature.

In operation then, the stabilizing temperature chosen is preferablyrelatively low. The windings of bridge circuit 2) are chosen so that thebridge will be balanced at the predetermined temperature, for example 30centigrade. If the temperature should fall below 36 centigrade, an AC.error signal will be sent through the amplifier to the windings of thebridge circuit, which also serve as a heater, to heat the inner chamberto 30 centigrade, at which time the bridge would again be balanced.

To assure that the inner chamber Will be maintained constant at thepredetermined temperature, the outer chamber must be cooled to atemperature at least as low as the predetermined temperature of theinner chamber, for example 30 centigrade. As a matter of practice,however, it is usually held a few degrees lower. Cooling is provided bythe thermoelectric cooling device 73, which device is energized throughvoltage comparator 95). As is Well known in the art, when direct currentis caused to flow through the cooling device in the proper direction,heat is removed from the vicinity of the cold junction. Thus, the outerchamber 36 is cooled by the thermoelectric cooling device.

The windings of bridge circuit 54 are selected so that the voltagecomparator will develop zero voltage (bridge in balance) only at apreselected temperature to indicate that the thermoelectric cooling unitneed take no more heat from the outer chamber. As can be readilyappreciated, ambient, or environmental, temperatures outside the outerchamber may be, for example, at any higher temperature so long as thethermoelectric cooling device has the capability to pull the temperatureat least to the predetermined temperature of the inner chamber.

If desired, the thermoelectric cooling device need not have a controlsystem associated therewith and could be constantly operated to pull thetemperature below the predetermined temperature of the inner oven. Thiswould mean, of course, that the heating coils of the inner oven mighthave to steadily heat the coils and possibly would have to supply agreat deal of heat if very low temperatures existed in the outerchamber.

From the foregoing, it should be evident to those skilled in the artthat the temperature compensated rnultichamber device of this inventionis particularly well suited for reliably maintaining a constanttemperature that can be either above or below environmentaltemperatures.

What is claimed as our invention is:

1. A compact multicharnber device having an automatic temperaturecontrol, said device comprising: first Wall means defining a firstenclosed chamber; means including a sensing and heating coil contiguousto said first wall means to sense temperature deviations from apreselected temperature value within said first chamber and responsivethereto heating said first chamber; second wall means surrounding saidfirst chamber and defining a second enclosed chamber; and meansincluding a thermoelectric cooling device contiguous to said second wallmeans for cooling said second chamber to a temperature at least as lowas, said preselected temperature whereby the temperature within saidfirst enclosed chamber s maintained constant even though environmentaltemperatures outside said second enclosed chamber are higher than saidpreselected temperature value.

2. An automatically temperature controlled and compact multichamberdevice, comprising: a first cylinder closed at both ends; a secondcylinder of larger diameter than the first and substantiallyconcentrically positioned with respect thereto, said second cylinderbeing closed at both ends; sensing and heating means including a bridgecircuit adjacent legs of which are dissimilarly affected by temperaturechanges whereby said bridge is unbalanced and produces an error signalwhenever the temperature within said first cylinder deviates from saidpredetermined temperature value, said error signal caus ng said firstcylinder to be heated whenever there is deviation in said temperature tothereby eliminate said error signal; cooling means including athermoelectric cooling device; and electrical circuit means for sensingthe temperature within said second cylinder and causing saidthermoelectric cooling device to lower the temperature in said secondcylinder it above a preselected temperature at least as low as thepredetermined temperature value to be maintained within said firstcylinder.

References Cited in the file of this patent UNITED STATES PATENTS1,940,599 Morrison Dec. 19, 1933 1,967,185 Clapp July 17, 1934 2,952,786Lewis Sept. 13, 1960 2,955,185 Cox Oct. 4, 1960 2,998,707 Meess et a1Sept. 5, 1961 FOREIGN PATENTS 144,669 Great Britain Sept. 9, 1921

1. A COMPACT MULTICHAMBER DEVICE HAVING AN AUTOMATIC TEMPERATURECONTROL, SAID DEVICE COMPRISING: FIRST WALL MEANS DEFINING A FIRSTENCLOSED CHAMBER; MEANS INCLUDING A SENSING AND HEATING COIL CONTIGUOUSTO SAID FIRST WALL MEANS TO SENSE TEMPERATURE DEVIATIONS FROM APRESELECTED TEMPERATURE VALUE WITHIN SAID FIRST CHAMBER AND RESPONSIVETHERETO HEATING SAID FIRST CHAMBER; SECOND WALL MEANS SURROUNDING SAIDFIRST CHAMBER AND DEFINING A SECOND ENCLOSED CHAMBER; AND MEANSINCLUDING A THERMOELECTRIC COOLING DEVICE CONTIGUOUS TO SAID SECOND WALLMEANS FOR COOLING SAID SECOND CHAMBER TO A TEMPERATURE AT LEAST AS LOWAS, SAID PRESELECTED TEMPERATURE WHEREBY THE TEMPERATURE WITHIN SAIDFIRST ENCLOSED CHAMBER IS MAINTAINED CONSTANT EVEN THOUGH ENVIRONMENTALTEMPERATURES OUTSIDE SAID SECOND ENCLOSED CHAMBER ARE HIGHER THAN SAIDPRESELECTED TEMPERATURE VALUE.